FIG. 1 shows an internal structure of a centrifuge described in Patent Literature 1 and, in FIG. 1, 1 denotes a rotary shaft whose shaft center coincides with a vertical direction and 2 denotes a rotary head attached to the upper part of the rotary shaft. Moreover, 3 denotes a rotor which is disposed in the upper part of the rotary head 2 and 4 denotes a lid that covers the upper part of the rotor 3.
The rotor 3 includes a plurality of sample insertion portions 5 and also includes, for example, rotor holes 6 and 7 into which the rotary head 2 is inserted, a frame 8, male members 9-1 and 9-2, and a guide pin 10. The rotor hole 6 is a circular hole with a fixed diameter, and the rotor hole 7 is formed as a circular hole whose diameter decreases toward the inside of the hole.
The male members 9-1 and 9-2 are rotatable about rotating shafts 11-1 and 11-2 horizontally disposed in the rotor hole 6, the centers of gravity are located below the rotating shafts 11-1 and 11-2, and the male members 9-1 and 9-2 have projections 13-1 and 13-2 on the sides opposite to a shaft center 12 of the rotary shaft 1 below the centers of gravity. The male members 9-1 and 9-2 are attached to the frame 8, and the frame 8 is attached to the rotor 3. The rotor 3 has through holes 14 and 15, and the through hole 15 formed in the frame 8 is screw-threaded.
The rotary head 2 includes, in the upper part thereof, a rotor coupling portion 16 and drive pins 17. The rotor coupling portion 16 has the shape of a cylinder whose center coincides with the shaft center 12 of the rotary shaft 1, and has a ring-shaped depression 18 in the inner side face thereof. The rotary head 2 includes a circular cylinder portion 19 that is fitted into the rotor hole 6 and a truncated cone portion 20 that is fitted into the rotor hole 7. The lid 4 has a knob 21 and a screw portion 22 for threaded engagement with the through hole 15 of the frame 8.
The guide pin 10 can move only between the drive pins 17, and, when the rotary head 2 rotates, power is transferred to the guide pin 10 from the drive pins 17 and the rotor 3 rotates. When the rotary head 2 stops, the rotor 3 stops with the rotary head 2.
When the rotor 3 is disposed on the rotary head 2 in a state in which the rotary shaft 1 is stopped, the centers of gravity of the male members 9-1 and 9-2 are located immediately below the rotating shafts 11-1 and 11-2, and, at this time, the male members 9-1 and 9-2 are located inside the rotor coupling portion 16.
When the rotary shaft 1 rotates, the male members 9-1 and 9-2 move by the centrifugal force in such a way that the projections 13-1 and 13-2 are fitted into the depression 18 and, if a force that separates the rotor 3 from the rotary head 2 (a force that causes the rotor 3 to rise) is applied when the projections 13-1 and 13-2 are fitted into the depression 18, in this example, a force is applied to the projections 13-1 and 13-2 in a direction in which the projections 13-1 and 13-2 are fitted into the depression 18. Thus, even when an unexpected force that separates the rotor 3 from the rotary head 2 is applied during rotation, the projections 13-1 and 13-2 and the depression 18 are not separated from each other, which makes it possible to achieve reliable fixation.